1. Field of the Invention
The invention relates to a nonaqueous electrolytic solution secondary battery, a current collector and a vehicle. In more detail, the invention relates to a nonaqueous electrolytic solution secondary battery applicable to an on-vehicle power source, and a current collector that can be used in the secondary battery.
2. Description of Related Art
A secondary battery is used as an on-vehicle power source that uses electricity as a driving source, or as a power source that is mounted on personal computers, portable terminals and other electric products. In particular, a lithium secondary battery and other nonaqueous electrolytic solution secondary batteries, which have light weight and can obtain high energy density, are preferable as an on-vehicle high output power source for electric vehicles and hybrid vehicles. In such a nonaqueous electrolytic solution secondary battery, a positive electrode includes a current collector and an active material layer, and as the current collector, typically Aluminum (Al) or an Al alloy is used. For example, in Japanese Patent Application Publication No. 2012-021205 (JP 2012-021205 A), with an object of combining the mechanical characteristics and low electric resistance performance, a current collector made of an Al foil in which Al content is 98% by mass or more and Fe and Cu are contained at specified ratios is proposed. In Japanese Patent Application Publication No. 2012-136736 (JP 2012-136736 A), a technique where in order to provide a current collector that is excellent in the tensile strength, Al plating is applied on a surface of a metal foil such as a Ni foil is proposed. In Japanese Patent Application Publication No. 2006-324143 (JP 2006-324143 A), a positive electrode terminal that is electrically connected to a positive electrode is disclosed. According to the positive electrode terminal, a part that is placed inside a battery is formed of high purity Al and other part is formed of a material having strength higher than that of the high purity Al, and it is intended to lengthen a life of the battery and to improve vibration resistance thereof thereby.
Incidentally, the nonaqueous electrolytic solution secondary battery described above is required to further improve performance such as high energy density. As one measure for realizing the high energy density, a use of a positive electrode active material that shows a higher operating potential is under study. However, in a nonaqueous electrolytic solution secondary battery that uses a positive electrode active material that shows an operating potential higher than 4.5 V based on metallic lithium (hereinafter, a potential based on metallic lithium is represented as “vs. Li/Li+” in some cases), when charge/discharge is repeated at a high potential, a battery capacity tends to largely decrease compared with a secondary battery of related art. It was clarified from a study of the present inventors that a degree of the decreasing tendency can vary depending on a positive electrode current collector. For example, in the secondary battery of concerned technology such as mentioned above, characteristics demanded on the current collector were mainly to combine conductivity and strength. According to the secondary battery of the related art described above, on a surface of Al or an Al alloy that mainly forms a current collector material, a coat of Al2O3 or AlF3 is formed. Since the coat is stable for a nonaqueous electrolytic solution, specified corrosion resistance is exerted. From this, in a use aspect that is assumed in a secondary battery that operates at a potential of the related art (typically, 4.2 V (vs. Li/Li+)), it was not considered that Al is eluted from the current collector and the battery capacity is decreased. For example, in Japanese Patent Application Publication No. 2012-021205 (JP 2012-021205 A) and Japanese Patent Application Publication No. 2012-136736 (JP 2012-136736 A), the related arts are disclosed.
However, in a nonaqueous electrolytic solution secondary battery that uses a positive electrode active material showing an operating potential higher than 4.5 V (vs. Li/Li+), depending on a use aspect, in spite of existence of the coat on a surface of the Al current collector, Al is eluted from the current collector, the eluted Al precipitates on the negative electrode and battery resistance increases, and the battery capacity may be decreased thereby.